Power and free roller conveyor systems are well known in the art. Such systems typically include a plurality of rotatable cylindrical rollers supported on a frame and defining a conveyor path along which objects may be conveyed. At least some of the rollers are powered in some way to cause them to rotate about their axes and thereby impart a driving force to any object supported thereon to cause it to be conveyed in a desired direction.
In a typical prior art system, an object to be conveyed will move along the conveyor path until it engages an obstacle, such as a stop that is movable into and out of the path of travel of the object. Once movement of the object has been arrested, the rollers that support the object will stop turning, although the remaining powered rollers will continue to rotate. Upon removal of the obstacle, the arrested object will continue its movement and the previously stopped rollers again will rotate.
Most of the known power and free roller conveyor systems utilize pulleys, sprocket wheels, or other mechanical drive transmitting devices coupled to the rollers to cause them to rotate. The pulleys or sprocket wheels are driven continuously by one or more electric motors via belts, chains, or the like. A clutch mechanism conventionally is incorporated between the driving pulley or wheel and each powered roller to enable the latter to stop turning while its pulley or wheel continues rotating.
Although such prior art constructions operate reasonably well for the purposes intended, a number of disadvantages are inherent in them. For instance, the clutch mechanisms can be complicated to manufacture, expensive to assemble, and troublesome to maintain. Further, many of the known constructions have rollers that are driven in one direction of rotation and cannot easily be driven in the reverse direction. In addition, many of the prior art systems, particularly those that use chain drives, are noisy.
In one prior art construction some of the rollers are powered by electrical induction motors of the kind wherein the rollers themselves serve as the rotors for the motors. In this construction only some of the rollers are provided with such an inductive drive while many, if not most, of the other rollers are not powered. This system suffers from many disadvantages that arise through an apparent compromise in its design. On the one hand, providing a motor for each roller is costly and possibly difficult to implement since each motor will differ to some extent from the others, thereby causing speed inconsistencies, uneven power distribution, and the like. On the other hand, the failure to provide drive means for each roller may cause the system to be underpowered and unsuitable for many applications.
In another prior art construction a linear induction motor is utilized to drive the conveyor, but the conveyor is not composed of rotatable rotors. In particular, the conveyor of this prior art construction has a secondary member of a linear inductive motor affixed thereto, and the primary member is mounted in a position in which it may interact with the secondary member to impart linear motion thereto. Although a number of different embodiments of such a system have been suggested, none of them has made use of rollers.
An object of the invention is to provide a power and free conveyor that substantially avoids the deficiencies of the prior art. In particular, such a conveyor should be relatively quiet and efficient in operation, require minimal maintenance, and provide drive power to all rollers as necessary while enabling any of the driven rollers to stop turning when movement of an object supported thereon is halted. Preferably, such a system enables an operator easily to reverse the direction of rotation of the driven rollers and further enables the operator to control the torque and the speed of rotation. Finally, such a system should be relatively easy to manufacture, simple in construction, and relatively inexpensive in comparison to the benefits attained. A conveyor constructed according to the invention possesses all of these characteristics.